If one of these criteria is met then repeat testing the following day is required for confirmation

Oral Glucose Tolerance Test (OGTT)

• Complicated test no longer recommended for routine use except in pregnancy

• Still available in many laboratories

• Still found in text books

• Used in testing in pregnancy

• This evaluates the endogenous insulin response to a physiological glucose challenge

• The diagnostic value of OGTT has been over estimated and is used too frequently in situations where it is not needed

• In the absence of a specific marker of the diabetic state the OGTT remains the most sensitive and practical test for the early recognition of asymptomatic diabetes, without fasting hyperglycaemia even if it is a non-specific test.

Indications of OGTT

• Evaluation of a person with a borderline elevation of fasting or post prandial plasma glucose

• Diagnosis of gestational D.M

• High risk individuals

• Evaluation of glycosuria

• Assessment of unexplained presence of what might be expected a diabetic complication e.g. Neuropahty

• Metabolic condition (elevated triglycerides)

• Obesity

• Clinical or epidemiological research projects

Preparation Of Patient For OGTT

• The patient must be ambulatory and free from pyrexia, acute illness or trauma for at least two weeks.

• He/she should have diet containing at least 150 g carbohyrate per day for three days prior to test

• Any drug that alter blood glucose level should also be discontinued prior to testing for 03 days.

• The test should be done in the morning

• The patient must have 8 – 16 h fast.

• Heavy tea and coffee drinkers should reduce their consumption

• Smoking should be avoided

• No physical exercise or activity is allowed

• Patient should be seated quietly and relaxed for 30 minute for test

Procedure For OGTT

• Glucose load

– For adults 75 g glucose

– For children 1.75 g/kg body weight

– Glucose load is given in water (25 g/dl)

• This blood samples are taken at half hourly interval up to 2 hours

• Urine samples are usually not required for the diagnosis of diabetes mellitus

Interpretation Of OGTT

• Normal

– Fasting < 5.5 mmol/l

– 0.5, 1.0, 1.5 hrs < 10 mmol/l

– 2 hrs sample < 7.8 mmol/l

• Diabetic

– Fasting > 7.8 mmol/l

– 2 hours or one intermediate

– Sample > 11.1 mmol/l

• Impaired OGTT

– Fasting < 5.5-7.8 mmol/l

– One intermediate sample > 11.1 mmol/l

– 2 hrs between 7.8 and 11.1 mmol/l

OGTT In Gestational D.M

• OGTT is done with a glucose load of 100g

• Blood samples are taken up to 3 hrs, at least two values must exceed the following

• Note: after 50 yrs of age; add 0.6 mmol per decade or 1 mg/year to the diagnostic criteria

Random Plasma Glucose

• In healthy individuals, plasma glucose conc. Vary only slightly throughout the day and generally are in the range of 2.5-7.3 mmol/l. The only rise that occurs is found following a meal.

• Diagnostic value

– > 11.1 mmol/l – dm

– < 2.5 mmol/l hypoglycaemia 7.8-11.1 mmol/l

– Further investigations

• Random glucose has no value in screening, diagnosis and follow up of DM

• It has greatest value in comatosed patients, whether known or preveiously unknown diabetes.

Post Challenge Plasma Glucose

• Glucose load = 75 g

• Plasma glucose conc. Is determined 2 hrs later

• It allows for more objective conditions of testing and a more precise comparison of an individual’s response with a large population. This test is more precise than a postraprandial glucose

• However this test requires more preparation

• Unrestricted activity

• Carbohydrate diet

• Fasting

• Diagnostic value – 11.1 mmol/l

Two Hour Postprandial Plasma Glucose

It has been used to screen for diabetes mell-itus, to diagnose diabetes and to monitor glucose control. The significance of the 2 hrs postprandial value is limited by the lack of rigidly controlled conditions

• Amount of carbohydrate

• Time used to consume meals

• Type of food

• Age of the patient

• Time of the day

These factors are responsible for the differences in the interpretation of the results

• Interpretation:

– Glucose value < 7.8 mmol/l normal

– Glucose value 7.8 – 11.1 mmol/l ogtt

– Glucose value >11.1 mmol/l dm

Sampling For Blood Glucose

A. Whole blood allowed to stand at room temperature shows decrease in glucose from 7-10% in one hour